Risk assessment basis of moving particles in gas insulated substations

Comprehensive acoustic measurements on bouncing particles in a gas insulated substation (GIS) have been carried out. The objective is to find parameters that both are available from external acoustic measurements and usable for assessing whether a particle has the potential to cause an insulation breakdown. The elapsed time between subsequent particle impacts is a measure of how far into the high-field region the particle can move, and thus also a measure on criticality. Secondly, the amplitude of the acoustic signal generated as a particle imparts the enclosure increases with increasing particle length and thus also with increasing criticality. Moreover, plotting these two parameters against each other (`particle flight time´ vs. `signal amplitude at impact´) for a significant number of impacts (e.g. 1000) always yields a very characteristic pattern, which in itself is a strong indication that the recorded signals are generated by one moving particle